Since koyukkuris lack stamina and resilience, almost every single ailment affecting adult yukkuris may have deathly effects in no time, with diarrhea, constipation and molds as the most common causes of an early demise of koyukkuris, save for physical accidents. Anti-yukkuritis is also a common occurrence, due to the feelings of abandonment a koyukkuri taken away from its early "easy place" (the pet shop) or its family may feel in the very first day of its new life as a pet yukkuri, the stress of being given a pet grade education (often a long process of flicks on the forehead and gentle reprimands due to their simple and childlike mindset) and the inability to deal with even mild stressful situation without the constant tutelage of a "parent figure". So, when the owner finds the Koyukkuri in the throes of Anti-Yukkuritis (trembling, faintly bemoaning its suffering without any physical ailment, calling upon its mommy, throwing up its filling, crying and refusing to move from its fluffy bed), the best course of action is keeping it from throwing up by pushing very gently the filling back in, petting the ko and lovingly praise it for its easiness, giving it orange juice to restore its strength and sweets to make it happy again.
The koyukkuri should now recover in no time and, if already able to speak, be able to explain its owner the causes of its depression. However, as a rule of thumb the most common causes are loneliness, being given a food overtly bitter, being left in an unclean place for too much time, being hurt with no one able to give it immediate care and comfort and damaging its accessory. As for the latter, it should be noted that pet koyukkuris need their accessories to reach "Easiness" as much as every other yukkuri does, and pet shops have a vast selection of replacement accessories for every size, age and type of yukkuri. Some Anons have experimented with the Yukkuri Belief Power, somewhat stronger in koyukkuris, by gently praising them and telling that their usual pitiful attempts to lick lick and "comfort" a broken accessory by begging it to heal are effective and useful. This lie has proven effective in a small number, allowing the koyukkuri to "magically" restore its accessory, the safest route is still replacing a torn of broken accessory when the koyukkuri is asleep, or by reassuring the koyukkuri that the owner was able to magically repair its original accessory, thus making it proud and certain about its inherent easiness.